Ungesättigte Zucker. Eine milde Sulfonat-β-Eliminierung bei Aminohexopyranosiduronat-Derivaten

Substituted 2-deoxy-2-acylamino-4-O-methanesulfonyl-hexopyranosiduronates yield, by mild alkaline mesylate (a, e)-β-elimination, the corresponding 4,5-unsaturated 4-deoxyhexopyranosiduronates VIII. This type of aminosugars proved to be the cyclic enol-ether acetal form of the 2,4-dideoxy-2-acylamino-hexos-5-ulosuronates. The structural principle of the latter can be found e.g. in neuraminic acid. These 4,5-unsaturated 4-deoxy-acylamino-hexopyranosiduronates give by reduction with NaBH₄ the corresponding 4,5-unsaturated 2,4-dideoxy-2-acylamino-hexopyranosides IX (with an endocyclic double bond on the glycosidic C atom 5). The isomeric 5,6-unsaturated 2,6-dideoxy-2-acylamino-hexopyranosides XVI (with an exocyclic double bond) are furthermore synthesized according to the method of HELFERICH [14] by elimination of a molecule of HI from the corresponding 2,6-dideoxy-2-acylamino-6-iodo-4-O-acylhexopyranoside derivatives XV. The ring stability of the two types of isomeric unsaturated hexopyranosides mentioned (bearing respectively an exo- and an endocyclic 5-enol-ether linkage) has been examined. In accordance with the stability principle of BROWN [16] – on the base of our preliminary experimental indications – the hexopyranosides with endocyclic double bond have been shown to be more stable than those with an exocyclic double bond: the latter (1) decompose slowly at 20°; (2) the α-glycosidic linkage is very easily split by dil. acetic acid at 20° within a few hours, giving 2, G-dideoxy-2-acyl-amino-D -xylo-hcxofuranos-5-ulose derivatives XX. On the other hand, the hcxopyranosides with endocyclic double bond show in the mass spectrometer, besides other fragmentations, a retro-dien decomposition. Some data on the NMR. spectra (100 and 220 MHz) of the above isomeric unsaturated acylamino-hexopyranosides (and hexopyranosiduronates, resp.) are furnished. The ORD./CD. spectra of the 4,5-unsaturated 2,4-dideoxy-2-acylamino-hexopyranosiduronates, which have two «COTTON centres», have been measured.     

Argentometric determination of iodide and cyanide using a depolarisation end-point

It has been shown that the depotarisation end-point technique, based on the phenomenon of a sudden out-of-balance current, produced by the establishment of a new redox potential at the indicator electrode in a pre-balanced circuit, can also be applied to precipitation titrations. The use of a platinum indicator electrode instead of one made of silver, and determination in very dilute solution, yield better results than those obtained using the classical potentiometric method.     

The oxonium theory in the light of an optical study of the hydrogen bond in some monovinyl ethers of glycols and polyglycols

Summary An optical investigation of some monovinyl ethers of glycols and polyglycols has indicated the presence of intermolecular hydrogen bonds in the liquid state, and this is confirmed by data derived from other phycicochemical investigations. The presence of an intermolecular hydrogen bond explains the anomalous valency of the oxygen atom of the investigated class of ethers (Its oxonium character), and also peculiarities of the properties of these ethers.     

Na-montmorillonite hydrates under ethane rich reservoirs: NPzzT and muPzzT simulations

Na-montmorillonite hydrates in presence of ethane molecules are studied by means of hybrid Monte Carlo simulations in the NP(zz)T and muP(zz)T ensembles. The NP(zz)T ensemble allows us to study the interlaminar distance as a function of water and ethane content. These data show clear plateaus for lower ethane contents and mainly for water contents consistent with the formation of a single water layer. In addition, from this ensemble the structure for some of these interlaminar compositions were analyzed. For systems containing few ethane molecules and water enough to complete a single layer, it was observed that ethane mainly situates close to the interlayer midplane and adopts a nearly parallel arrangement to the clay surface. On the other hand, the muP(zz)T ensemble allows us to determine the interlaminar distance and water-ethane content for any specific reservoir. Here, some important findings are the following: the partial exchange of water by ethane molecules that enhances for decreasing the water vapor pressure; the obtention of a practically constant interlaminar space distance as a function of the water vapor pressure; the conservation of ion solvation shells; the enhancement of the water-ethane exchange for burial conditions; and finally, the incapability for a dehydrated clay mineral to swell in a dry and rich ethane atmosphere.     

Kinetics of Addition of Alcohols to 3-Aroyl-2,4-dihydro-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones

The kinetics of the reaction of 3-aroyl-2,4-dihydro-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones with aliphatic alcohols in toluene at 25°C were studied by spectrophotometry. The effects of electronic and steric factors in the nucleophile and substrate were estimated by treatment of the kinetic results by the Hammett and Taft equations.     

Chemical and thermal analysis of the biopolymers in thyme (Thymus vulgaris)

Thyme (Thymus vulgaris) has been known, long time ago, for its aromatic properties. It contains essential oils and polymers such as cellulose (mixture of hemicellulose and cellulose) and lignin. The thyme, studied in this work, was gathered from the same place, in the period from November 1999 to October 2000. The chemical analysis (water, total ash, essential oils, extractive substances, cellulose, holocellulose and lignin) can be used roughly in the characterisation of the four periods that correspond to the four seasons of the year. The cellulose level was found to be more than lignin level in the wet periods (growth of the plant). The opposite was found in the dry periods. The total ash and essential oil levels were found to be high during the period of high pluviometry. The thermal decomposition of cellulose and holocellulose was found to fit well with the first-order kinetics. The activation energy, under air flow, was 185 and 196 kJ mol⁻¹ for cellulose and holocellulose, respectively. The maximum decomposition rate and thermal analysis heating rate of lignin were found to have a direct linear relationship.     

Consequence of boar edible tissue consumption on urinary profiles of nandrolone metabolites. II. Identification and quantification of 19-norsteroids responsible for 19-norandrosterone and 19-noretiocholanolone excretion in human urine

In previous work (Le Bizec et al., Rapid Commun. Mass Spectrom. 2000; 14: 1058), it was demonstrated that a boar meal intake could lead to possible false accusations of abuse of 17beta-nortestosterone in antidoping control. The aim of the present study was to identify and quantify endogenous 19-norsteroids in boar edible tissue at concentrations that can alter the steroid urinary profile in humans, and lead to excretion of 19-norandrosterone (19-NA) and 19-noretiocholanolone (19-NE). The samples were analysed in two laboratories. The methodologies used for extraction and detection (GC/MS(EI) and LC/MS/MS(APCI+)) are compared and discussed. 19-Norandrostenedione (NAED), 17beta- and 17alpha-nortestosterone (bNT, aNT), and 17beta- and 17alpha-testosterone (bT, aT) were quantified. The largest concentrations of NAED and bNT were observed in testicles (83 and 172 microg/kg), liver (17 and 63 microg/kg) and kidney (45 and 38 microg/kg). A correlation between the bNT and NAED content of a typical meal prepared with boar parts and the excreted concentrations of 19-NA and 19-NE in human urine was demonstrated.     

Synergism in the solvent extraction of samarium by thenoyltrifluoroacetone and triphenyl or trioctyl phosphine oxide mixture

Synergistic extraction of samarium with TTA(HA) and TPPO or TOPO (B) mixtures were investigated. The extracted complex was proved to have the general formula SmA₃ · 2B. A graphical determination for the formation constants of these complexes gave the values 3.9 × 10¹³ and 8.2 × 10¹⁰ for SmA₃ · 2TOPO and SmA₃ · 2TPPO in benzene, respectively.     

Almost constant sequences and well-distribution in compact groups

We study the properties of sequences (c _n ) in a compact groupG such that (x _n ) being (weakly) well-distributed implies (c _n x _n ) being (weakly) well-distributed and give a complete characterisation in terms of almost constant sequences as well as a generalisation to non-compact locally compact groups.     

A generalization of second variation

f p- , l p . p=1 . . p - , f -.